Relationships of foliar carbon isotope composition (delta C-13) with foliar C, N, P, K, Ca, Mg contents and their ratios of 219 C-3 species leaf samples, obtained in August in 2004 to 2007 from 82 high altitude grassland sites on the Qinghai-Tibet Plateau China, were examined. This was done with reference to the proposition that foliar delta C-13 increases with altitude and separately for the life-form groups of graminoids, forbs and shrubs and for the genera Stipa and Kobresia. For all samples, foliar delta C-13 was negatively related to foliar K, P and Sigma(K+ Ca+ Mg), and positively correlated to foliar C, C/N and C/P. The significance of these correlations differed for the taxonomic and life-form groups. Lack of a relationship of foliar delta C-13 with foliar N was inconsistent with the majority of studies that have shown foliar delta C-13 to be positively related to foliar N due to a decrease of C-i/C-a (the ratio between intercellular and atmospheric concentration of CO2) and explained as a result of greater photosynthetic capacity at higher foliar N concentration. However this inconsistency relates to other high altitude studies that have found that photosynthetic capacity remains constant as foliar N increases. After accounting for the altitudinal relationship with foliar delta C-13, of the elements only the K effect was significant and was most strongly expressed for Kobresia. It is concluded that factors critical to plant survival and growth at very high altitudes, such as low atmospheric pressure and low temperatures, may preclude expression of relationships between foliar delta C-13 and foliar elements that have been observed at lower altitudes.
